1. Field of The Invention
This invention relates, generally, to hydraulic nonmechanical pumping devices for transferring material, and specifically, to an air-assisted liquid jet pump for moving solid materials.
2. Description of Related Art
The dredging industry commonly utilizes large centrifugal pumps for suction and movement of slurry material, i.e., water containing varying particle sizes such as sand or gravel. Because of the abrasive effect caused by particles, these pumps suffer wear and tear and significant downtime to repair parts of the equipment.
Removal of solid materials from a water environment by means of hydraulic operations is well known in the art. Dredging and deep sea mining operations employ water forced through piping configurations to cause an upward flow that pulls the water and solid material from the desired location.
A common problem in using jet eductor systems occurs because high pressure water jets, while effective at removing high volumes of slurry material, cause severe cavitation in the throat and mixing regions of the eductor conduit, and result in lowered efficiency and extremely short equipment life, as discussed in U.S. Pat. No. 4,165,571.
Use of air to induce upward flow of water has also been used. Use has typically involved compressed air or gas, requiring expensive compression equipment. In addition, the combination of gas, water and solids has contributed to process instability in the mixing chamber of the device, as discussed in U.S. Pat. No. 4,681,372.
Jet eduction systems have used atmospheric air for the purpose of creating air bubbles for separation processes in U.S. Pat. No. 5,811,013. These systems were not designed to increase pump efficiency, prevent pump cavitation or increase pump flow as disclosed by the present invention. Prior art teaches against introduction of air for these purposes.
Cavitation is the term used to describe vapor bubble generation and collapse in pumps when the pressure in the pump suction drops to or below the NPSH for the pump. The same effects can be observed when air enters the liquid stream inlet of a pump. The presence of a gas in both circumstances causes reduced capacity, reduced or unstable head pressure, and unstable power consumption. Vibration, noise, accelerated corrosion, fatigue failure and other mechanical damage are the consequences of cavitation. The use of the term cavitation in this specification is intended to cover the resulting effects rather than define the physical circumstances causing these resulting effects.